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What is a 51% attack on the Blockchain? + Video

A 51% (51% ATTACK) attack on digital currency networks, such as Bitcoin, occurs when an individual or entity can acquire more than 50% of the processing power of a network (hashtag). This allows the Blockchaink to be manipulated. In this article, you will get acquainted with 51% attack and its different angles in simple language.

Before we get into the 51% attack, we need to know a little bit about digital currency mining and the blockchain network that underpins digital currencies. One of the great features of Bitcoin and its blockchain network is that everyone can participate in block building and transaction verification. People who validate transactions and blocks on the Bitcoin network are called nodes. Miners or miners in the bitcoin network are one of the main nodes. The decentralized operation of the nodes ensures that everyone follows the rules of the Bitcoin protocol correctly and that all participants in the network agree with the current state of the Blockchain. This means that in order for the extraction process to work properly and the transactions to be done correctly, the majority of the participants must reach a consensus.

Bitcoin consensus algorithm is Proof Of Work. This algorithm, which is the scientific name of mining, ensures that miners can only verify the validity of a block if all network participants collectively confirm that the answer to the block equation (block hash) found by the miner is correct.

Bitcoin blockchain infrastructure, as a decentralized head office and distributed system, prevents the network from being centrally controlled by an entity. That is why no centralized power controls bitcoin.

Because digital currency extraction with a proof-of-work protocol requires large financial investments to provide electricity and computing power, the performance of a miner is calculated based on the amount of computing power it provides to the network. This power is commonly referred to as the hash rate. Many miners are in different locations and compete for valid hashes for the new block to get the reward of block extraction. In such cases, the hash rate is distributed to several nodes, which means that the hash rate is not available to any single individual or entity, or at least not intended to be.

But what happens if the hash rate is not sufficiently distributed? What happens if an entity can capture more than 50% of the network hash rate? One of the most important consequences of such an event is what we call a “51% attack” or a “majority attack.” Then with the help of articles from websites بایننس‌آکادمی، Inostopedia And Afxampire You will become familiar with this concept.

What is a 51% attack?

Attack 51% A potential attack on a blockchain network is one in which a single individual or entity takes over the majority of the network hash rate, so that it can disrupt network activity. In such a scenario, the attacker would have enough extraction power to intentionally delete or manipulate transactions. An attacker can also return a transaction that has been approved in the past, which ultimately leads to the problem of “double spending”.

Also a Attack of the majority A successful attacker allows the attacker to refuse to approve some or all of the transactions. In addition, the attacker can prevent some or all of the miners from extracting, an act known as “mining monopoly.”

But by attacking the majority, the attacker will not be able to return transactions that were approved long ago. Also, the attacker can not change the reward for extracting each block, generate new coins out of the protocol and steal coins that do not belong to him. It is impossible to cause such disruptions in the network by a 51% attack.

What is the probability of a 51% attack?

A 51% attack on large blockchains like Bitcoin is almost impossible because it has no economic justification.

Because the Blockchain is a distributed network of nodes, all participants participate in the consensus-building process. This is one of the reasons for the high security of Bitcoin. The larger the network and the more powerful its nodes, the better the protection against attacks and the easier it is to prevent data manipulation.

In the proof of work mechanism, if a miner has a higher hash rate, he has a better chance of finding a valid solution to the next block problem. Block extraction requires countless efforts, and more computing power means more effort per second. In the early days of Bitcoin, only a few miners were involved in growing the network and making it more secure. But with the rise in bitcoin prices, many miners have entered the network to compete for blockchain rewards. This competitive scenario is another bitcoin security factor. So while miners can extract bitcoins and make money using computing resources, it does not make sense to use these resources to disrupt the network.

Therefore, a 51% attack on Bitcoin is very unlikely due to the size of the network. When a Blockchaink is large enough, the likelihood that an individual or group of people will be able to have the computing power needed to overcome others.

What is a 51% attack on the Blockchain?  + Video

In addition, as the network grows, it becomes more difficult to change previous blocks and manipulate the transactions of those blocks, because the blocks are interconnected. Because of this, the more approvals a block has, the harder it will be to change the block or return transactions. Thus, a 51% successful attack can only disrupt the network in a short period of time and affect only the last few block transactions.

51% attack with non-financial motives

Imagine another scenario in which a bad actor, without any financial motive, attacks the Bitcoin network and tries to destroy the network at a high cost. If such an attacker can successfully attack and disrupt the network, the bitcoin software and protocol will respond quickly to the attack and adapt to the new conditions. Of course, this compatibility requires other nodes to quickly reach a consensus on these changes. Of course, in an emergency, reaching a quick agreement is not out of reach. Bitcoin is very resistant to attacks and is the safest and most secure digital currency available.

51% attack on Altcoins

It is very difficult to get a lot of computing power for a 51% attack on the Bitcoin network, but it is not difficult to get a lot of computing power for a 51% attack in smaller digital currencies. Compared to Bitcoin, blockchain (post-bitcoin digital currencies) has a lower hash rate. The hash rate of some altcoins is so low that a 51% attack is practically possible. Verge, Mona Quinn, Bitcoin Gold and Zenkash are among the digital currencies that have fallen victim to the majority attack.

In May 2018 (May 97), one or a group of actors maliciously attacked the Bitcoin Gold network. At the time, Bitcoin Gold was the 26th largest digital currency. The attacker was able to capture most of the network hash rate for a few days, and by returning and re-spending some coins, he acquired a number of $ 18 million Bitcoin bitcoins.

34% attack

Tangel is a distributed general ledger that is fundamentally different from the Blockchain, but is designed to achieve similar goals. The Tangle network has been used in the development of Iota, a digital currency for use on the Internet of Things.

Due to the structural difference between Tangel and the Blockchaink, the majority can be attacked with 34% (more than one third) of the computing power of Tangel network.

Concerns about increasing the influence of extractive device manufacturers

Recently, there have been growing concerns about the growing power of mining hardware companies. Manufacturers of ASIC devices have drastically increased the number of devices produced and, at the same time, have constantly updated the technology used in these devices. This has increased their role in bitcoin mining and has worried bitcoin developers.

The number and quality of devices, most of which are manufactured by a few specific companies, has made these companies, which also have a lot of financial power, have a lot of influence in the network. Such power allows these companies the potential to launch a 51% attack on the network.

What is a 51% attack or a majority attack?
Most of the miners in the world use bitcoin machines.

Rising concerns have prompted Monroe developers to refrain from using ISIC devices on the network by updating the digital currency protocol. Some other digital currencies also intend to abandon the proof of work protocol in their new updates and use the “stock proof” protocol. Ethereum, the second best digital currency on the market, is one of these digital currencies that is about to be updated to Ethereum 2.0. With this update, mining will end with graphic pebbles in the Ethereum network and stock proof will replace it.


A majority attack, or 51%, refers to a malicious player disrupting the Blockchain network. In this phenomenon, an attacker can disrupt the network for a while and manipulate transactions and blocks by taking over more than half of the hashtag blockchain in networks that use the proof-of-work protocol.

The larger the network of a Blockchaink, the 51% more difficult to attack in practice. For this reason, Bitcoin, the largest digital currency with the widest network of nodes, is highly resistant to this attack. But altcoins with smaller networks are vulnerable to this attack, and so far several altcoins have fallen victim to the majority attack.


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